A printing ink is generally formulated according to strict performance requirements demanded by its intended market application and desired properties. Whether formulated for office printing or for production printing, a particular ink is expected to produce images that are robust and durable under stress conditions, such as exposure to abrasive or sharp objects or actions that produce a crease defect in the image (such as folding or scratching the imaged paper). For example, in a typical design of a piezoelectric ink jet device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Hot melt inks that are typically used with ink jet piezoelectric printers have a wax based ink vehicle, e.g., a crystalline wax. Such solid ink jet inks provide vivid color images. In such systems, these crystalline wax inks partially cool on an intermediate transfer member and are then pressed into the image receiving medium such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents show through on the paper. However, the use of crystalline waxes places some limitations on ink performance, for example the brittleness of crystalline materials may reduce the ink's robustness properties that are required to provide abrasion-resistant images. Consequently, inks that are formulated to have increased mechanical robustness properties are attractive materials.
There are several approaches on how to improve the robustness of solid inks. However, the right solution could be one that utilizes a new specialized material component that has not been explored for inks, but that have shown promise when used in other composite materials and applications. An example of such an enabling material is the POSS macromolecule, which are known to form self-assembled nanostructures. POSS is known as Polyhedral Oligomeric Silsesquioxanes, a family of molecularly precise organosilicon compounds that have a cubic structure comprised of a Si8O12 cage-like core and surrounded by eight functional organic groups that can be variable in structure, represented by the groups (which can be the same or different) in the following structure:
The POSS molecule itself has an approximate diameter of 1-3 nm in cases when the eight R groups are organic groups of less than about 6 carbons in length (for example, when the groups are cycloaliphatic groups such as cyclopentyl, or linear alkyl groups with less than 6 carbons such as iso-propyl), whereby the cubic silsesquioxane unit can be regarded as nearly “spherical” in shape.
POSS compounds have been reportedly used to synthesize polymer nanocomposite materials that function to reinforce polymeric binder materials such as epoxy resins, and are known to provide enhanced strengthening properties to materials (See J. D. Lichtenhan, cited above), in a similar manner as polymer-clay nanocomposites. However the disadvantages with using nanoclay materials as reinforcing fillers are the challenges with energy-intensive top-down processing that is needed to disperse the individual, exfoliated clay layers or platelets within the polymer binder. Alternatively, by using a nanoscale material component such as POSS that can be dispersed at the molecular level, one can take advantage of a self-assembly process to build a nanostructured layer that may function as the reinforcing filler component for a binder material, with the potential to produce nanocomposite materials having enhanced mechanical properties. Many substituted POSS compounds having a wide variety of organic R-groups and functional groups are commercially available from Hybrid Plastics Inc., and some have been investigated for various uses.
There remains a need for specialized components and/or composite materials that can be formulated in wax-based solid inks or other inks as reinforcing fillers that will enable improved mechanical robustness of the ink.